With the development of modern mobile communication and microwave communication as well as demands for high-performance, low-noise and low-cost radio frequency (RF) components, traditional silicon devices can no longer meet new requirements on technical specifications, output power and linearity. Therefore, SiGe HBT devices have been proposed which play an important role in the applications of high-frequency power amplifiers. Compared with gallium arsenide (GaAs) devices, though SiGe HBT devices are at a disadvantage in frequency performance, they can well solve the issue of heat dissipation accompanying with power amplification, benefiting from their better thermal conductivities and good mechanical capacities of their substrates. Moreover, SiGe HBT devices also have better linearity and higher integration level. Further, SiGe HBT devices are well compatible with the conventional silicon process and still belong to the silicon-based technology and the complementary metal oxide semiconductor (CMOS) process, thus reducing manufacturing cost. For these reasons, the SiGe BiCMOS (bipolar complementary metal oxide semiconductor) process provides great convenience for the integration of power amplifiers and logic control circuits.
Currently, SiGe HBT devices have been widely adopted internationally as components for low-noise amplifier (LNA) circuits employed in front-end amplifier circuits of signal receiving systems, such as global positioning systems. For LNA circuits, the most critical factor is their high-frequency noise figures. Although the noise performance of an LNA circuit is also affected by whether the circuit is properly designed, the most determining factor is the intrinsic noise characteristics of the devices. To improve the intrinsic noise performance of a device in high-frequency applications, it is an important approach to improve its noise isolation property.